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ORGANIC CHEMISTRY I

• HYDROCARBONS• NOMENCLATURE• REACTIONS• Chapter 23 (McM)• Chapter 15.1-15.2 Silberberg

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Chapter 15

Organic Compounds and the

Atomic Properties of Carbon

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Organic Compounds and the Atomic Properties of Carbon

15.1 The Special Nature of Carbon and the Characteristics of Organic Molecules

15.2 The Structures and Classes of Hydrocarbons

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Goals & Objectives

• See the Learning Objectives on page 618.

• Understand these Concepts:• 15.1-6.

• Master these Skills:• 15.1-2.

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Organic Chemistry

• study of the compounds of carbon

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Bonding Properties of Carbon

• Carbon forms covalent bonds in all its elemental forms and compounds.– The ground state electron configuration of C is [He]2s22p2; the

formation of carbon ions is therefore energetically unfavorable.

– C has an electronegativity of 2.5, which is midway between that of most metals and nonmetals. C prefers to share electrons.

• Carbon exhibits catenation, the ability to bond to itself and form stable chain, ring, and branched compounds.– The small size of the C atom allows it to form short, strong

bonds.

– The tetrahedral shape of the C atom allows catenation.

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Figure 15.1 The position of carbon in the periodic table.

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Comparison of Carbon and Silicon

• As atomic size increases down the group, bonds between identical atoms become longer and weaker.– A C–C bond is much stronger than a Si–Si bond.

• The bond energies of a C–C bond, a C–O bond, and a C–Cl bond are very similar.– C compounds can undergo a variety of reactions and remain

stable, while Si compounds cannot.

• Si has low energy d orbitals available for reaction, allowing Si compounds to be more reactive than C compounds.

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Diversity and Reactivity of Organic Molecules

• Many organic compounds contain heteroatoms, atoms other than C and H.– The most common of these are O, N, and the halogens.

• Most reactions involve the interaction of electron rich area in one molecule with an electron poor site in another.– C–C bonds and C–H bonds tend to be unreactive.

– Bonds between C and a heteroatom are usually polar, creating an imbalance in electron density and providing a site for reactions to occur.

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Hydrocarbons

• contain only carbon and hydrogen• Saturated--contain the maximum amount

of hydrogen--contain only single bonds• Unsaturated--do not contain the

maximum amount of hydrogen--contain double and/or triple bonds

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Hydrocarbons

• Cyclic compounds--contain rings in the structure

• Aromatic compounds--includes benzene and its derivatives--special class of compounds

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Drawing Carbon Skeletons

Each C atom can form a maximum of four bonds.These may be four single bonds, OR one double and two single bonds, OR one triple and one single bond.

The arrangement of C atoms determines the skeleton, so a straight chain and a bent chain represent the same skeleton.

Groups joined by a single bond can rotate freely, so a branch pointing down is the same as one point up.

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Figure 15.4 Adding the H-atom skin to the C-atom skeleton.

A C atom single-bonded to one other atom gets three H atoms.

C C

H

H

HA C atom single-bonded to two other atoms gets two H atoms.

C C

H

C

H

A C atom single-bonded to three other atoms gets one H atom.

C C

H

C

C

A C atom single-bonded to four other atoms is already fully bonded (no H atoms).

C C C

C

C

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Figure 15.4 continued

A double-bonded C atom is treated as if it were bonded to two other atoms.

C C H

H

A double- and single-bonded C atom or a triple-bonded C atom is treated as if it were bonded to three other atoms.

C C

H

C

C C H

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Sample Problem 15.1 Drawing Hydrocarbons

PLAN: In each case, we draw the longest carbon chain first and then work down to smaller chains with branches at different points along them. Then we add H atoms to give each C a total of four bonds.

PROBLEM: Draw structures that have different atom arrangements for hydrocarbons with

(a) Six C atoms, no multiple bonds, and no rings

(b) Four C atoms, one double bond, and no rings

(c) Four C atoms, no multiple bonds, and one ring

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Sample Problem 15.1

(a) Six carbons, no rings

H C C C C C C

H

H

H

H

H

H

H

H

H

H

H

H

H6-C chain

H C C C C C H

H

H

HC

H

H

H

H

H H

HH

H

5-C chain

H C C C C H

H

H

HC

C

H

H H

HH

H

H H

H

C C C C H

H

H

H

C

C

HH H

H

H

H

H

H H

H

4-C chains

H C C C C C H

H

H

H

C

H

H

H

H

H

HH H

H

5-C chain

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Sample Problem 15.1

(b) Four C atoms, one double bond, and no rings

H C

H

H

C C

H

H

CH H

H

3-C chain

H C C C C

H

H

H H H

H

H

C C

H

H

H

H

H

C C H

HH

4-C chains

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Sample Problem 15.1

(c) Compounds with four C atoms and one ring

C C

CC

H

H

H

H

H

H

H

H

C C

C

H H

C

H

H

HHH

H

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Alkanes

Hydrocarbons contain only C and H. Alkanes are hydrocarbons that contain only single bonds and are referred to as saturated hydrocarbons.

The general formula for an alkane is CnH2n+2, where n is any positive integer.

Alkanes comprise a homologous series, a group of compounds in which each member differs from the next by a –CH2– group.

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Hydrocarbons

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Alkanes

• simplest saturated hydrocarbons• general formula CnH2n+2

• first member of the alkane series is methane, CH4

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Naming Organic Compounds

The root name of the compound is determined from the number of C atoms in the longest continuous chain.

The name of any organic compound is comprised of three portions:

PREFIX + ROOT + SUFFIX

The prefix identifies any groups attached to the main chain.

The suffix indicates the type of organic compound, and is placed after the root.The suffix for an alkane is –ane.

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Table 15.1 Numerical Roots for Carbon Chains and Branches

Roots Number of C Atoms

meth- 1

eth- 2

prop- 3

but- 4

pent- 5

hex- 6

hept- 7

oct- 8

non- 9

dec- 10

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Figure 15.5 Ways of depicting the alkane 3-ethyl-2-methylhexane.

C C C C C

H

H

H

C

C

HH H

C

H

H

H

H H

H

H H

H

C

H

H

H

H

H

Expanded formula

CH3 CH

CH3

CH

CH2

CH3

CH2 CH2 CH3

Condensed formula

Carbon-skeleton formula Ball-and-stick model Space-filling model

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Isomers

compounds having the same molecular formula but with different structural formulas

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Constitutional Isomers

Constitutional or structural isomers have the same molecular formula but a different arrangement of the bonded atoms.

A straight-chain alkane may have many branched structural isomers.

Structural isomers are different compounds and have different properties.If the isomers contain the same functional groups, their properties will still be similar.

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Isomers

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Isomers

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Table 15.3 The Constitutional Isomers of C4H10 and C5H12

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Figure 15.7 Formulas, molar masses (in g/mol), structures, and boiling points (at 1 atm pressure) of the first 10 unbranched alkanes.

Alkanes are nonpolar and their physical properties are determined by the dispersion forces between their molecules.

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Isomers

• C7H16 -- 9 isomers

• C10H22 -- 75 isomers

• C15H32 -- 4,347 isomers

• C30H62 -- 4,111,846,763 isomers

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Nomenclature of Alkanes

• Name the following compound using the IUPAC system of nomenclature.

• CH3CH2CHCH3

• CH3

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Nomenclature of Alkanes

• 1. Choose the longest chain of carbon atoms in the structure and give that chain the name of the member of the alkane series having the same number of carbon atoms.– butane

• 2. Number the C atoms in that longest chain starting at the end that will give the smallest number at the substituted position.

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Nomenclature of Alkanes

• 3. Precede the parent name with the position number and name of each substituting group.

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Substituting Groups

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Nomenclature of Alkanes

• CH3CH2CHCH3

• CH3

• 2-methylbutane

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Nomenclature of Alkanes

• 4. Separate numbers from numbers with commas and numbers from words with hyphens.

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Nomenclature of Alkanes

• Give IUPAC names for each of the following compounds

• Draw the isomers and give the IUPAC name of the possible isomers of C6H14

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Alkenes

A hydrocarbon that contains at least one C=C bond is called an alkene.

Alkenes are unsaturated and have the general formula CnH2n.

To name an alkene, the root name is determined by the number of C atoms in the longest chain that also contains the double bond.The C chain is numbered from the end closest to the double bond.The suffix for alkenes is –ene.

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Unsaturated Hydrocarbons

• 1. Alkenes, CnH2n

– contain C=C– CH2=CH2 ethene

– CH3CH=CH2 propene

– CH3CH2CH=CH2 1-butene

– CH3CH=CHCH3 2-butene

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Geometric Isomers

The double bond of an alkene restricts rotation, so that the relative positions of the atoms attached to the double bond are fixed.

Alkenes may exist as geometric or cis-trans isomers, which differ in the orientation of the groups attached to the double bond.

Geometric isomers have different physical properties.

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Table 15.4 The Geometric Isomers of 2-Butene

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Alkynes

An alkyne is a hydrocarbon that contains at least one CΞC triple bond.

Alkynes have the general formula CnH2n-2 and they are also considred unsaturated carbons.

Alkynes are named in the same way as alkenes, using the suffix –yne.

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Unsaturated Hydrocarbons

• 2. Alkynes, CnH2n-2

– contain carbon-carbon triple bonds– C2H2

– C3H4

– C4H6

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Sample Problem 15.2 Naming Alkanes, Alkenes, and Alkynes

PROBLEM: Give the systematic name for each of the following, indicate the chiral center in part (d), and draw two geometric isomers for part (e).

CH3 C

CH3

CH3

CH2 CH3

(a) (b)

CH3 CH2 CH

CH3

CH

CH2

CH3

CH3

(c)

(d)

CH3 CH2 CH

CH3

CH CH2

(e)

CH3 CH2 CH C

CH3

CH CH3

CH3

PLAN: For (a) to (c), we find the longest continuous chain (root) and add the suffix –ane because there are only single bonds. Then we name the branches, numbering the C chain from the end closest to the first branch. For (d) and (e) the longest chain must include the double bond.

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Sample Problem 15.2

SOLUTION:

2,3-dimethylbutane

(b)

CH3 CH2 CH

CH3

CH

CH2

CH3

CH3

methyl

1

23456

hexane

methyl

3,4-dimethylhexanemethyl

12

34

5

(c)

ethyl

1-ethyl-2-methylcyclopentane

CH3 C

CH3

CH3

CH2 CH3

(a)

butane

methyl

methyl1 2 3 4

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Sample Problem 15.2

3-methyl-1-pentene

(d)

CH3 CH2 CH

CH3

CH CH2

methyl

12345

chiral center

1-pentene

(e)

12

3456

C CCH3

CH

H

CH2

CH3

CH3CH3

12

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56 C CCH3

CH

CH2

H

CH3

CH3

CH3

methyl

methyl

methyl

methyl

3-hexene

cis-2,3-dimethyl-3-hexene trans-2,3-dimethyl-3-hexene

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Nomenclature of Alkanes

• Give IUPAC names for each of the following compounds

• Draw the isomers and give the IUPAC name of the possible isomers of C5H12

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Cyclic Hydrocarbons – CnH2n

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Figure 15.6

Depicting cycloalkanes

C

C C

H H

H

HH

H

C

C C

CH

H

H

H

H

H H

H

cyclopropanecyclobutane

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Figure 15.6

Depicting cycloalkanes

cyclopentane cyclohexane

C C

CC

C

H HH

H

HHH

HH

H C

CC

C

CC

H H

H H

H

HH

H

H

H

HH

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Aromatic Hydrocarbons

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Figure 15.13 Representations of benzene.

Resonance forms having alternating single and double bonds.

or

Resonance hybrid shows the delocalized electrons as either an unbroken or a dashed circle.

Benzene is an aromatic hydrocarbon.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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methylbenzene(toluene)

bp = 110.6°C

1,2-dimethylbenzene(o-xylene)

bp = 144.4°C

1,3-dimethylbenzene(m-xylene)

bp = 139.1°C

1,4-dimethylbenzene(p-xylene)

bp = 138.3°C

O2N NO2

NO2

2,4,6-trinitromethylbenzene(trinitrotoluene, TNT)

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Tools of the Laboratory Nuclear Magnetic Resonance (NMR) Spectroscopy

Figure B15.1 The basis of proton spin resonance.

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Tools of the Laboratory

Figure B15.2 The 1H-NMR spectrum of acetone.

Nuclear Magnetic Resonance (NMR) Spectroscopy

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Tools of the Laboratory

Figure B15.3 The 1H-NMR spectrum of dimethoxymethane.

Nuclear Magnetic Resonance (NMR) Spectroscopy

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Tools of the Laboratory

Figure B15.4 An MRI scan showing a brain tumor.

Nuclear Magnetic Resonance (NMR) Spectroscopy

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Dr . Kay Sandberg’s Nomenclature Presentation from NC State

• The presentation can be reached at the following link:

• http://courses.ncsu.edu/ch221/common/kas/Alkane_Nomenclature/Alkane-Nomenclature.html

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